Voltage Drop Calculator
Naesun Code (Korea's interior wiring code) 1410-1 formula e = (k × L × I) / (1000 × A), judged side by side against its distance-based limit (3% / 5% / 6% / 7%) and the Korean Electrical Code (KEC) 232.3.9 limits by supply type.
Result
Enter circuit information and click Calculate.
Voltage Drop Limits & Wire Size by Distance
The most-searched values in one place. Left: the regulatory limit. Right: which cross-section actually clears it.
Allowed Voltage Drop by Distance (Naesun Code)
| Run length | Allowed drop |
|---|---|
| up to 60m | 3% |
| over 60m – 120m | 5% |
| over 120m – 200m | 6% |
| over 200m | 7% |
KEC 232.3.9 Allowed Voltage Drop (by supply type)
| Supply type | Lighting | Other |
|---|---|---|
| Low-voltage supply | 3% | 5% |
| High-voltage or higher supply | 6% | 8% |
High-voltage or higher supply: for the part of the user's wiring beyond 100m, the limit may rise by 0.005% per metre, by at most 0.5%.
Drop by Distance × Cross-section (220V single-phase 2-wire · 20A · copper)
Each cell is the voltage drop percentage. Cells marked ▲ (bold red) exceed the Naesun Code limit for that distance.
| Distance | 2.5sq | 4sq | 6sq | 10sq | 16sq | 25sq |
|---|---|---|---|---|---|---|
| 10m | 1.3% | 0.8% | 0.5% | 0.3% | 0.2% | 0.1% |
| 20m | 2.6% | 1.6% | 1.1% | 0.6% | 0.4% | 0.3% |
| 30m | 3.9% over | 2.4% | 1.6% | 1.0% | 0.6% | 0.4% |
| 50m | 6.5% over | 4.0% over | 2.7% | 1.6% | 1.0% | 0.6% |
| 80m | 10.4% over | 6.5% over | 4.3% | 2.6% | 1.6% | 1.0% |
| 100m | 12.9% over | 8.1% over | 5.4% over | 3.2% | 2.0% | 1.3% |
| 150m | 19.4% over | 12.1% over | 8.1% over | 4.9% | 3.0% | 1.9% |
| 200m | 25.9% over | 16.2% over | 10.8% over | 6.5% over | 4.0% | 2.6% |
The matrix assumes the fixed conditions above. Different voltage, current, phase type or conductor material changes the result — use the calculator for actual design. Aluminum drops about 1.6× more under the same conditions.
Basis: Naesun Code 1410-1 (Korea's interior wiring code — drop limit by distance) · Korean Electrical Code (KEC) 232.3.9 (December 2023 revision) · KS C IEC 60364
What this tool does
The Voltage Drop Calculator takes conductor cross-section, current, run length, and phase type, then computes the voltage drop (V) and drop percentage (%) and compares it against the distance-based allowable limits in Naesun Code 1410-1 (Korea's interior wiring code). Choose the supply type (low voltage, or high voltage and higher) and the load type (lighting or other) and it also judges the result against the KEC 232.3.9 limits side by side, flagging it when the two standards disagree. It supports both copper and aluminum conductors and applies the correct coefficient for single-phase 2-wire, single-phase 3-wire, 3-phase 3-wire, and 3-phase 4-wire circuits. Use it to confirm whether a wire gauge is adequate for the run distance and whether the voltage at the far end stays within equipment tolerance.
Who uses this
- Check whether the drop exceeds the limit when a load is far from the distribution panel
- Decide whether to step up to a larger wire gauge because of excessive drop
- Compare voltage drop between single-phase and 3-phase wiring options
- Assess the extra drop when using aluminum conductors instead of copper
- Learn the voltage-drop formula for Korean electrician licensing exams
How to use (5 steps)
- 1Enter the line (or phase) voltage (V) and load current (A) — e.g., 220V single-phase, 380V 3-phase.
- 2Enter the run length (m, one-way) — the actual wire length from the panel to the load.
- 3Select the conductor cross-section (㎟) from the KS standard sizes, the conductor material (copper/aluminum), and the phase type (single-2, single-3, 3-phase-3, 3-phase-4).
- 4For the KEC check, choose the supply type (low voltage / high voltage or higher) and the load type (lighting / other). Low-voltage supply and other loads are preselected.
- 5Read the voltage drop (V), drop percentage (%), and the pass/fail verdict against both the Naesun Code distance limit and the KEC limit. If it fails, increase the cross-section or shorten the run.
Formula & basis (Naesun Code 1410-1 · KEC 232.3.9)
■ Voltage drop e = (coefficient × L × I) ÷ (1000 × A) L = run length (m, one-way), I = current (A), A = cross-section (㎟) ■ Coefficient by phase type (copper) Single-phase 2-wire 35.6 3-phase 3-wire 30.8 Single-phase 3-wire / 3-phase 4-wire 17.8 Aluminum conductor: coefficient × 1.6 ■ Drop percentage e(%) = (e ÷ V) × 100 ■ Allowable drop by distance ≤ 60m — 3% / ≤ 120m — 5% / ≤ 200m — 6% / > 200m — 7% ■ KEC allowable drop (Table 232.3-1, by supply type × load) Low-voltage supply — lighting 3% / other 5% High-voltage or higher supply — lighting 6% / other 8% High-voltage or higher supply, user's wiring beyond 100m — +0.005% per metre (at most +0.5%)
Worked examples
Example 1: 220V single-phase, 20A, 50m, 4㎟ copper
e = (35.6 × 50 × 20) ÷ (1000 × 4) = 8.9V. Drop = 8.9 ÷ 220 × 100 ≈ 4.05%. The ≤60m limit is 3%, so this fails against the distance table. The same 4.05% reads differently under KEC 232.3.9: it passes on a low-voltage supply for non-lighting loads (5%) but exceeds the 3% limit for lighting. Increasing to 6㎟ or larger brings it down to about 2.7% and passes.
Example 2: 380V 3-phase 3-wire, 30A, 80m, 10㎟ copper
e = (30.8 × 80 × 30) ÷ (1000 × 10) = 7.39V. Drop = 7.39 ÷ 380 × 100 ≈ 1.95%. Within the ≤120m limit of 5%, so it passes.
Example 3: switching from copper to aluminum
Same as Example 1 but aluminum: coefficient 35.6 × 1.6 = 56.96 → e ≈ 14.24V, drop ≈ 6.47%. Aluminum's lower conductivity raises the drop by about 60% at the same gauge — you must size up at least one step.
Frequently asked questions
Is the run length one-way or round-trip?
Enter the one-way length (panel to load). The return current path is already accounted for in the phase coefficients (35.6, 30.8, 17.8), so do not double the distance.
What are the 3% / 5% allowable limits based on?
They come from Naesun Code 1410-1 (Korea's interior wiring code): 3% for runs ≤60m, 5% for ≤120m, 6% for ≤200m, 7% over 200m. Check the Naesun Code text for the scope they apply to (feeder only, or feeder plus branch circuits). The values exist to keep lighting and equipment within their normal operating voltage. For reference, KEC (Korean Electrical Code) 232.3.9 sets limits on the voltage drop from the service entrance to the equipment in a consumer installation that depend mainly on how power is supplied, not on distance (December 2023 revision; check the current text for later amendments). On a low-voltage supply the limits are 3% for lighting and 5% for other uses; on a high-voltage or higher supply (above 1 kV AC under KEC) they are 6% and 8%, although the drop within the final circuit should preferably stay within the low-voltage values (3% and 5%). According to the note attached to the high-voltage row of the table, the limit may be raised by 0.005% per metre for the part of the user's wiring beyond 100m, by at most 0.5%. A larger drop is also allowed while a motor is starting or for other equipment with a high inrush current (232.3.9, item 2). This calculator judges against the Naesun Code 1410-1 distance table and the KEC limits by type of supply side by side; they are separate standards with different structures, so the results are not merged. For an installation supplied at low voltage, some bands of the distance table are looser than the KEC limits (3% lighting, 5% other) — beyond 60m for lighting and beyond 120m for other uses — so the two verdicts can differ; check your design documents or the client's requirement for which one applies. Meeting the stricter one satisfies both. Note that KEC measures the total drop from the service entrance to the equipment (feeder plus branch circuits), so a calculation for a single section comes out lower than that total. The allowance beyond 100m treats the distance you enter as the user's wiring length and applies only to high-voltage or higher supply.
What should I do if the drop exceeds the limit?
Either (1) step up the conductor cross-section, (2) shorten the run by relocating the panel, or (3) switch single-phase to 3-phase (lower coefficient). Increasing the wire gauge is the most common fix.
Why does aluminum wire have a larger voltage drop?
Aluminum's conductivity is about 61% of copper's, so at the same cross-section its resistance — and voltage drop — is roughly 1.6× higher. This calculator applies a ×1.6 factor automatically when aluminum is selected. To match copper's drop, size aluminum one or two steps larger.
Does it account for DC or power factor?
This is a simplified AC calculation assuming a power factor of 1, ignoring line reactance (inductance). Long, high-current, or low-power-factor circuits are more affected by reactance — use a licensed engineer or design software for precise work.
Cautions
- •Simplified AC calculation assuming power factor 1 and ignoring reactance. Precise design needs full line-impedance calculation.
- •Enter the one-way length; the round-trip path is already in the phase coefficient.
- •The tool shows the Naesun Code 1410-1 distance bands and the KEC 232.3.9 limits by supply type side by side. If they disagree, follow the one your design documents or client require; actual design also depends on feeder/branch allocation and equipment characteristics.
- •KEC measures the total drop from the service entrance to the equipment (feeder plus branch circuits). One section entered alone comes out lower than that total, so add up the drop percentages of each section. A larger drop may be allowed while a motor starts.
- •Reference calculation only. Have an electrical safety manager or qualified engineer review actual installations.
- •Cross-section must be a KS standard size.
Related forms
Last reviewed: 2026-10-07
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